The electroerosive wire-cutting process, as the term is generally recognized in the art, makes use of a continuous wire electrode composed of, say, copper or brass and in a regular thin wire form, i.e. circular in cross section, and having a diameter ranging between 0.05 and 0.5 mm. The wire is mounted in a wire-support structure to extend from a supply site, e.g. a wire supply reel or drum, to a collection site, e.g. a wire takeup reel or drum and is axially transported by drive means, e.g. a traction roller arrangement located in the collection site, to travel along a guided continuous path and to move continuously through a cutting zone. A workpiece disposed in the cutting zone is juxtaposed with the moving wire to define a machining gap therewith which is flooded with a machining liquid medium. An electrical machining current is passed between the moving wire constituting a tool electrode and the workpiece constituting a counter-electrode to electroerosively remove material from the workpiece. Meanwhile, the workpiece is displaced relative to the moving wire electrode generally transversely to the axis thereof along a predetermined path so that a desired wire-cut pattern determined by the path of relative displacement is generated in the workpiece. The term "electroerosive" or "electroerosion" is used herein to refer to a machining process wherein material removal is effected as a result of passage through the machining gap of a high-density electrical current which may take the form of a succession of discrete, time-spaced electrical discharges which occur at a high frequency, or the form of a strong electrolytic solubilization current which may either be continuous or pulsed, or a combination of the action of electrical discharge with the electrolytic solubilization action. Depending upon the particular action of material removal desired, the machining liquid has a composition enabling it to act as dielectric, conductive or dielectric/conductive gap medium. Water may be deionized or rendered ionic to various extents to present a favorable EDM (electrical discharge machining), ECM (electrochemical machining) or ECDM (electrochemical-discharge machining) liquid medium. The gap flushed with the machining liquid must be of a small size, generally in the order of microns, to establish and maintain the electroerosive gap condition between the moving wire electrode and the workpiece. The continuous axial movement of the wire electrode provides continuous renewal of the machining surface thereon juxtaposed with the workpiece across the machining gap and is required because the wire electrode must be thin as before mentioned.
The basic principle of the wire-cutting electroerosion process is therefore to achieve a desired pattern of cut or to shape the pattern by effecting the corresponding patterning or contouring feed between the workpiece and a "line" (i.e. linear) electrode constituted by the wire. This is a basic distinction from the sinking-type electroerosion process in which the tool electrode is shaped and the electrode shape is reproduced in the workpiece. In the wire-cutting electroerosion process there is no analogy between the contour of the wire electrode and a desired pattern of cut to be formed in the workpiece. The "line" electrode effectively follows a prescribed path in the workpiece which directly produces the desired pattern of cut. Therefore the accuracy of a wire-cut pattern is affected by the accuracy of the contouring feed path prescribed and followed in the relative movement between the wire electrode and the workpiece. There has been no recognition in the art that the shape of the wire electrode may affect the accuracy of a wire-cut pattern in the workpiece. Accordingly it has been generally believed that it suffices to use a wire electrode of circular or regular cross-section which is readily available in sufficient thickness or as thin as 0.05 to 0.5 mm in order to achieve a desired accuracy since the accuracy is dependent on the question of precisely setting a contouring feed path and having the wire electrode precisely follow the precision-set path.